Name: pipe pressure drop from wall friction
Uploaded: 2025-02-13T15:43:35.000Z
Duration: 1 min 28 s
Channel: JoVE

Consider a fluid flowing through a pipe; it encounters frictional resistance, causing energy losses known as major losses, resulting in a pressure drop along the pipe&#39;s length.
Fluid flow can be laminar or turbulent. In laminar flow, the fluid moves smoothly, and resistance depends on viscosity. In turbulent flow, chaotic motion with swirling eddies makes the pressure drop dependent on viscosity and pipe wall roughness.
Pressure drop depends on various factors, including viscosity, density, velocity, pipe dimensions, and surface roughness.
These factors are often analyzed using dimensionless numbers like the Reynolds number and relative roughness to characterize flow behavior.
The friction factor is crucial for calculating pressure drops in turbulent flow. It depends on the Reynolds number and relative roughness and is often determined using the Moody chart, which categorizes flow regimes.
The Darcy-Weisbach equation uses the friction factor to quantify energy loss. Engineers often use empirical equations like the Colebrook equation for accuracy, though they require iteration or approximations like the Haaland equation.
Even smooth pipes experience friction loss due to the no-slip condition. Over time, corrosion increases roughness, exacerbating pressure losses.

major losses in pipes

Major Losses in Pipes

When a fluid flows through a pipe, it experiences energy losses due to frictional resistance along the pipe walls, known as major losses. These energy losses result in a pressure drop, which varies based on the flow conditions &#8212; whether laminar or turbulent &#8212; and the specific physical properties of the fluid and pipe.
Fluid flow can be classified as laminar or turbulent, primarily based on the Reynolds number. This dimensionless number reflects the relative influence of inertial to viscous forces in the fluid. In laminar flow (Re &#60; 2000), the fluid flows in parallel layers, or streamlines, with minimal cross-stream mixing. Here, the pressure drop mostly depends on the fluid's viscosity and is generally lower. In contrast, turbulent flow (Re &#62; 4000) is characterized by chaotic eddies and swirling motions. In this regime, the pressure drop is influenced not only by viscosity but also by the roughness of the pipe wall, as these irregularities disrupt the flow further, increasing energy losses.
The pressure drop in a pipe depends on several factors: fluid properties, flow velocity, pipe characteristics, and dimensionless numbers.
The Darcy-Weisbach equation is the standard approach for quantifying the pressure drop due to frictional losses in pipe flow:
<img alt="Fluid mechanics equation, &#916;P=f(L/D)(&#961;v&#178;/2), pressure loss calculation." src="/files/ftp_upload/18080/18080_Equation_1.svg" style="text-align: center; height: 30px;" data-altupdatedat="1762173717000" data-alt="Equation 1" />
Where:
<ol style="list-style-type: circle;">
	<li>&#916;P is the pressure drop,</li>
	<li>f is the friction factor,</li>
	<li>L is the length of the pipe,</li>
	<li>D is the pipe diameter,</li>
	<li>&#961; is the fluid density,</li>
	<li>v is the flow velocity.</li>
</ol>
The friction factor f is crucial for calculating pressure drops, especially in turbulent flow. It depends on the Reynolds number and the relative roughness of the pipe. Engineers often refer to the Moody chart, which provides empirical values of friction factors across flow regimes and roughness levels.
The Colebrook equation
<img alt="Darcy-Weisbach equation, fluid flow formula with friction factor, diagram for hydraulic analysis." src="/files/ftp_upload/18080/18080_Equation_2.svg" style="text-align: center; height: 30px;" data-altupdatedat="1762173717000" data-alt="Equation 2" />
Where:
<ol style="list-style-type: circle;">
	<li>f is the friction factor,</li>
	<li>&#1013;/D is the relative roughness</li>
	<li>Re is the Reynolds number.</li>
</ol>
offers a precise method to calculate f for smooth and moderately rough pipes, but it is implicit and requires iterative solutions. To avoid iteration, approximations like the Haaland equation:
<img alt="Darcy-Weisbach equation, fluid flow friction factor formula, scientific calculation." src="/files/ftp_upload/18080/18080_Equation_3.svg" style="text-align: center; height: 30px;" data-altupdatedat="1762173717000" data-alt="Equation 3" />
Where:
<ol style="list-style-type: circle;">
	<li>f is the friction factor,</li>
	<li>&#1013;/D is the relative roughness</li>
	<li>Re is the Reynolds number.</li>
</ol>
are commonly used in practice, providing reasonably accurate friction factor values without extensive calculation. Understanding these dynamics enables engineers to design pipe systems that manage flow efficiently, compensating for potential pressure losses over time as pipe roughness increases.

Consider &#160;a fluid flowing through a pipe; it encounters frictional resistance, causing energy losses known as major losses, resulting in a pressure ...

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Civil Engineering

Unit 1

Flow in Pipes

KEY TERMS AND CONCEPTS

pipe pressure drop from wall friction

Pipe pressure drop from wall friction is a major loss in fluid flow. As a fluid moves through a pipe, friction along the pipe walls removes energy. That energy loss shows up as a drop in pressure. The size of the drop depends on the flow conditions and on the physical properties of both the fluid and the pipe.

Flow in a pipe is often described as laminar or turbulent using the Reynolds number. This dimensionless number compares inertial forces with viscous forces in the fluid. In laminar flow, which occurs when Re is less than 2000, the fluid moves in parallel layers with little mixing across the streamlines. In this case, the pressure drop depends mostly on viscosity and is usually lower.

Turbulent flow occurs when Re is greater than 4000. It has chaotic eddies and swirling motion. In this regime, pressure drop depends on viscosity and on the roughness of the pipe wall. Those surface irregularities disturb the flow and increase energy losses.

Engineers estimate pipe pressure drop with the Darcy-Weisbach equation. In this relation, ΔP is the pressure drop, f is the friction factor, L is the pipe length, D is the pipe diameter, ρ is the fluid density, and v is the flow velocity. The friction factor is especially important in turbulent flow. It depends on the Reynolds number and on the pipe’s relative roughness.

To find friction factors, engineers often use the Moody chart. It gives empirical values across flow regimes and roughness levels. The Colebrook equation gives a more precise value for smooth and moderately rough pipes, but it is implicit and usually needs iteration. To avoid repeated calculations, the Haaland equation is commonly used as an approximation and gives reasonably accurate friction factor values.

Pipe Pressure Drop from Wall Friction

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Pipe pressure drop from wall friction is a major loss in fluid flow. As a fluid moves through a pipe, friction along the pipe walls removes energy. That energy loss shows up as a drop in pressure. The size of the drop depends on the flow conditions and on the physical properties of both the fluid and the pipe. Flow in a pipe is often described as laminar or turbulent using the Reynolds number. This dimensionless number compares inertial forces with viscous forces in the fluid. In laminar flow,...

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key terms and concepts

Learn how wall friction causes pressure drop in pipes, how Reynolds number separates laminar and turbulent flow, and how Darcy-Weisbach, Moody, and Colebrook are used.

Pipe Pressure Drop from Wall Friction | JoVE K12

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civil engineering

Pipe Pressure Drop from Wall Friction

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